Field of the Invention
The invention relates to a method of driving a capacitive actuator of a fuel injection valve of an internal combustion engine in a manner such that a constant stroke or displacement is obtained.
Various methods of driving capacitive actuators, in particular piezoelectric actuators, are known. When driving with a prescribed, constant amount of energy, the actuator may either execute a corresponding stroke or displacement or exert a specific force.
In the case of the valve concepts used for fuel injection valves and the tuning chosen at the same time, when there is low fuel pressure a low amount of energy is required to ensure a specific motion (elongation) of the capacitive actuator or the valve needle. When there is high fuel pressure, a great force is required at an early time in order to achieve rapid opening of the valve. This leads to the following problems when driving the actuator with a constant amount of energy:
The characteristic curves of the amounts of fuel for various fuel pressures cross one another, which makes the use of adaptive methods more difficult. At moderate and high fuel pressure, ensuring a very small amount of fuel is made more difficult, since the minimum driving time of the actuator cannot go below a certain value. In the operating range predominantly used, a higher amount of energy is supplied to the actuator than is required. This influences the service life of the actuator and the mechanical drive elements of the fuel injection valve and consequently their reliability.
It is accordingly an object of the invention to provide a method which overcomes the hereinafore-mentioned disadvantages of the heretofore-known methods of this general type in such a way that it is possible to supply the actuator with the amount of energy required for a desired stroke in every operating range and, as a result, to extend the service life of the actuator and of the mechanical drive elements of the fuel injection valve and to consequently increase their reliability.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of driving a capacitive actuator of a fuel injection valve of an internal combustion engine for achieving a constant stroke of the actuator, which includes determining an amount of energy that is supplied to the actuator in dependence on the fuel pressure acting on the actuator.
Rather than supplying a constant amount of energy to the actuator for a driving operation to achieve a desired stroke, the amount of energy is determined in dependence on the fuel pressure.
A constant stroke or displacement of the actuator in the entire operating range of the internal combustion engine is desirable in order to restrict the number of parameters required for determining the amount of injected fuel which is to be supplied to the internal combustion engine.
A desired amount of energy is supplied to the actuator by applying a charging voltage which is assigned to this amount of energy and is additionally dependent on the capacitance of the actuator at the time, or, when the charging voltage is known, by applying this voltage for a prescribed charging time.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method of driving a capacitive actuator of a fuel injection valve of an internal combustion engine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.